Alex,
As many know I am a "recovering" marketing guy. I've lived and breathed transactional marketing roles at companies like McDonald's Corp (cash register rings) and Turner Broadcasting (over night ratings) ... along with many others ... for over 25 years.
One thing that has always been the case is that most consumers, most of the time, can more easily grasp ideas that are simpler and nearer to them. Most people (believe it or not) have a more difficult time forecasting what they'll be doing over a month's time vs. a week.
So the answer to your question, initially, is that I was using my consumer marketing experience.
However, as a coworking space owner, I served up a variety of usage schemes during the early days. Maybe it's market specific, but I could sense in my conversations that people felt they were getting a better value by paying a monthly fee for X days per week. 10X per month doesn't sound like many days ... but 2X per week does (even though it's less).
So, ultimately - no formal research. Just general consumer marketing psychology + coworking experimentation.
Curios - have you tried both ways and found monthly to be more successful?
Cheers